Service Life Assessment of Electrodes and Joints Structure for Aluminum Alloy Resistance Spot Welding

To investigate the influence of spherical and planar electrode structures on its service life and the joint structure of aluminum alloy resistance spot welding, experiments were conducted on a 1.5 mm-thick 5A02 aluminum alloy plate by employing the three-phase secondary rectificified resistance spot welding machine with power of 300 kVA, with chromium zirconium copper alloy as the electrode material. The spherical electrode and planar electrode end face dimensions were SR100 mm and ϕ7 mm, respectively. The results show that the spherical electrode life is longer than that of the planar electrode. Under single grinding condition, 75 welding points can be achieved and the joint quality meets the requirements of the U.S. military standard. The maximum tensile force of the welded joint is 4.429 kN, with the core diameter of 5.194 mm. The solder core is composed of fine equiaxed grains at the center and cylindrical crystals around. The alloying trend of spherical electrode and welded aluminum alloy plate is weak, resulting in small element diffusion depth. The hardness of the tip surface after welding changes in an oblique “N” shape with the depth, and restores to the original hardness of electrode at 3.0 mm away from the tip surface.